Mouse Ly-6 molecules are implicated in the control of lymphocyte differentiation and activation, and are encoded by members of a multigene family. No human homologue has yet been identified. Molecules related to Ly-6 will be sought in human T-cells. Since low stringency hybridizations with Ly-6cDNA probes have failed to identify human genetic homologues, biochemically related proteins will be sought: Candidate T-cell surface proteins identified on the basis of phosphatidylinositol (PI)-attachment will be characterized structurally and functionally. 1. Mouse monoclonal antibodies (MAbs) will be generated with specificity for human T-cell plasma membrane proteins which are released by PI-specific phospholipases C (PI-PLC). 2. The antibodies will be screened for ability to inhibit or enhance T-cell proliferation under conditions analagous to those effective with anti-Ly-6 MAbs. 3. In parallel with the above, a novel two-dimensional electrophoretic system will be employed to identify those plasma membrane proteins with covalent PI attachments. Those showing properties similar to Ly-6 molecules will be chosen for purification and characterization. 4. Proteins which by functional and/or biochemical criteria are similar to Ly-6 molecules will be purified. Affinity chromatography will facilitate purification of those for which MAbs are available, otherwise the ability to alter the molecules' properties by enzymic removal of diacylglycerol will be exploited along with conventional purification procedures. 5. Amino acid sequence data will be obtained. 6. Based on these, oligonucleotide probes will be synthesized for use in isolation of the corresponding cDNAs. The cDNA and amino acid sequences will permit analysis of homology with Ly-7. The T-cell subsets and molecular subsystems to which PI-proteins belong will be identified and their interactions studied. A long- term goal will be to reconstruct functional subsystems in non-T- cells by gene transfection.